1. Field of the Invention
The present invention relates generally to inkjet printheads, and more particularly to methods for designing ink delivery manifolds employed with page wide printheads.
2. Description of the Related Art
Printers, copiers and other related reproduction equipment often employ printheads to deposit ink onto a print medium to provide readable characters and images. A programmed controller is often utilized to rasterize the print data and couple the same to the printhead to cause droplets of ink to be deposited on the print medium in the form of characters, such as letters, symbols, images, etc. Printheads are typically constructed with a number of miniature nozzles that are electrically addressable to cause ink to be jetted from desired nozzles to form the characters on the print medium. In practice, a printhead includes a heater chip with plural chambers where the ink can be nucleated into a drop and ejected therefrom, a nozzle plate attached to the heater chip to form the droplet of ink, an ink manifold to route the ink to the heater chip, and an ink supply of some type, whether it be a cartridge or ink tank.
Reproduction equipment utilizing inkjet printheads often use a single printhead that is moved back and forth in a swath laterally across the print medium to deposit ink dots in desired positions along a line. Once each line of ink dots is printed, the print medium is incrementally advanced to print another sequence of ink dots. As a number of lines of ink dots are incrementally printed on the medium, a string of letters or other characters is formed. Each additional string of characters is formed in the same manner, namely alternately moving the printhead in a swath across the print medium and incrementally advancing the paper.
Another technique for printing characters is to employ a page wide printhead which extends laterally across the width of the print medium. With this technique, the page wide printhead does not move, but rather prints a single line of ink dots substantially simultaneously. Then, the print medium is advanced so that a subsequent line of ink dots can be printed. As can be appreciated, the use of the page wide printhead significantly reduces the time required to print a string or page of characters, as the printhead does not have to be scanned across the width of the print medium.
While the utilization of a page wide printhead is an efficient method for quickly printing many characters, the construction of such type of printheads is more complicated and thus more costly and prone to manufacturing errors. Many of the components of a printhead, especially the heater chip and the manifold, are constructed using semiconductor wafers and corresponding processing techniques. As such, the fabrication of a page wide printhead for standard letter-size paper, requires a printhead having a lateral length of about eight and one-half inches. In this instance, the conventional practice is to use a number of individual heater chips that are mounted on a support that spans the width of the print medium. The heater chips are staggered or offset so that a standard space exists between the last nozzle of one heater chip and the first nozzle of the adjacent heater chip. The spacing between each printable ink dot in a line is thus the same, even between adjacent (and staggered) heater chips. Liquid ink is applied to a long and narrow ink via on the top side of the heater chip, where the ink is supplied internally in the heater chip to the many heater chambers. Each heater chamber includes a heater (often a resistor) for each nozzle that is addressable by the print controller to heat the ink in the respective chamber and nucleate the same so that it is jetted downwardly through the nozzle plate onto the print medium.
In addition to heater chips, a manifold is required in order to couple the liquid ink from a reservoir to the backside ink trenches and thus to the various heater chambers of each heater chip. When printing characters in color, the heater chip employs a row of heater chambers and an ink via for each color. The manifold construction is correspondingly more complicated when printing characters in color. If, for example, magenta, yellow, cyan and black ink colors are utilized for the primary colors to print an image of any color, then the manifold must have at least four different ink channels to accommodate the four different colors of ink. Moreover, the different ink channels must be extended to the various backside ink trenches of the individual heater chips. It can thus be appreciated that the construction of the ink manifold is complicated, in that very small channels must be formed in circuitous paths in the manifold to couple the liquid ink to the individual heater chamber structures of the heater chips. Owing to the fact that the individual heater chips can each have hundreds of heater chambers and corresponding nozzles, the ink delivery manifold can be challenging to manufacture.
Because of its complexity, a manifold for routing liquid ink from a source to the backside ink trenches of the heater chip is often constructed of a semiconductor material which can be processed with micron-size features. The manifold typically includes ink ports on the top surface to mate to the ink supply, and elongate ink channels of the bottom surface to mate with the backside ink trenches of the underlying heater chip. For purposes of efficiency, the manifold can be made in a top half and a bottom half, with each half etched to form the desired features, such as ink ports in the top half and the ink channels in the bottom half. At least one manifold half is formed so that the desired ink ports are in liquid communication with the desired ink channels. The manifold halves can then be bonded together so that when liquid ink of a certain color is applied to a top ink port, it is routed internally in the manifold to a specified ink channel on the bottom. Accordingly, the different colors of ink are efficiently supplied to the specified ink channels and thus to the corresponding backside ink trenches of the heater chip. However, even when manufacturing manifolds for page wide printheads, the semiconductor material of the manifold can be as long as the print medium is wide. In other words, the semiconductor manifold can be made eight and one-half inches long for printing on a letter-size page.
The design trend is to make the semiconductor heater chips, which together comprise a major part of the printhead, smaller in size without compromising performance. The price of a heater chip generally corresponds to the size of the semiconductor material from which it is made, as the smaller the semiconductor chip, the more chips can be made from a wafer of a give size. Similarly, as the size of the heater chip is reduced, the features are also reduced in size. One feature of a heater chip that is sensitive to size are backside ink trenches which channel the liquid ink to the heater chambers of the heater chip. In other words, if the sizes of the backside ink trenches in the heater chips are simply scaled down the ability to maintain the volume flow rate of ink to the heater and nozzle structures is reduced. With a smaller cross-sectional size of an ink channel, the volume flow rate of ink can be restricted and the efficiency of the printhead will be compromised.
The design of ink manifold, and especially the surface thereof that mates to the heater chip, must have the same shape and size features as that of the heater chip to which it is mated. When features of the heater chip are made smaller, then the ink delivery features on the bottom surface of the ink manifold that mates with the heater chip should also be made of comparable size and location so that when the two are mated together, the volume flow rate of ink is not restricted between the two printhead components. As noted above, the ink manifold has ink delivery channels on the bottom side thereof which mate with the backside ink trenches on the top of the heater chip. The manifold also has ink ports on the top side for mating with a base member, or other structure in liquid communication with the ink supply. The placement and size of the ink ports formed in the manifold is also of concern when scaling the size of the components, as the ink port design can be optimized to allow a sufficient amount of ink to be delivered without choking the supply of ink.
As the size of the semiconductor components of a printhead are scaled down, the spacing of the features thereof is also made smaller. For example, not only are some of the features, such as the ink ports and channels made smaller, but the distance between each port and between each channel is made smaller. There is a practical limit in making the features closer together, as the bonding agent that adheres the manifold to the heater chip requires a certain minimum surface area to be spread or dispensed thereon, so that the bonding agent does not run into the port or channel structures. When the manifold and heater chip are bonded together with an adhesive, the process is usually carried out using robotic devices which apply the adhesive through a syringe-type device around the various features, and then the pieces are placed together until the adhesive has set and cured. As can be appreciated, the accuracy by which the robotic mechanism can apply a specified amount of adhesive has practical limits, and thus the fabrication of the manifold and the heater chip must accommodate the inaccuracies inherent in the adhesive-applying process. Often, an entire wafer of manifold structures is bonded to a wafer of heater chips, and then the components are cut from the composite wafer as individual units.
From the foregoing, it can thus be seen that a need exists for a technique to make a semiconductor manifold for an ink jet printhead that is cost effective and with optimized features for ink delivery. Another need exists for a technique for fabricating an ink delivery manifold having many ink ports for each ink channel to thereby allow a large volume of ink to be carried therethrough. Another need exists to better utilize the area of a semiconductor wafer, and facilitate assembly of the printhead components.